Digital plate maker system and method

ABSTRACT

Graphics and text data are combined selectively to discharge incremental areas of a charged electrophotographic member to form thereon a latent text and/or graphics image represented by the graphics and text data, the imaged member thereafter being toned and output from the system so that the toned image may be fused on the member and the member may be used as a printing plate in an offset lithographic printing press. The apparatus includes an optical system that may form a maximum of 22 individual rays which are deflected twice through a field flattening lens and then onto the charged member. The optical system further includes an optical scale or grating which provides electrical signals indicating the precise location of the individual rays along scan lines on the member. The apparatus further includes an electronic system which generates electrical signals from the graphics and text data to form the 22 individual rays. The text data is used to modulate signals produced by the graphics data, the result of the modulation being beam control signals used to form the 22 individual rays. The apparatus further includes a toning system that provides a vertical meniscus of toning fluid, the meniscus being essentially stationary with the electrophotographic member as the electrophotographic member is rotated past the toning station.

This application is a division of application Ser. No. 139,462, filedApr. 11, 1980, now U.S. Pat. No. 4,408,868.

CROSS REFERENCE TO RELATED APPLICATION AND PATENT

Reference is made to a co-pending application Ser. No. 11,320 filed Feb.13, 1979 now U.S. Pat. No. 4,468,706, and entitled "DIGITAL LASER PLATEMAKER AND METHOD", the applicant being Lysle D. Cahill.

Reference is also made herein to a U.S. Pat. No. 4,025,339 issued on May24, 1979 to Manfred R. Kuehnle.

Both the application and the patent above identified are owned by theAssignee of the application herein.

FIELD AND BACKGROUND OF THE INVENTION

The field of the invention comprises apparatus and methods for imagingelectrophographic members by means of radiant energy devices such aslasers, the imaged electrophotographic members being thereafter used forprinting. In the case of lithographic offset printing, the imaged memberitself is treated to render toned and untoned parts hydrophobic andhydrophilic, respectively, and the member comprises the printing platewithout further processing. In other cases, the tonedelectrophotographic member may be used as an information source byreading the images or projecting them if transparent or photographicallyreproducing them if desired. The preferred use of the invention is tomake printing plates upon metal substrates such as stainless steel.These substrates are coated with a type of photoconductive coating whichwill be described hereinbelow.

In the printing industry, printing plates for printing both graphics andtext have in the past been produced manually with the graphics imagesbeing reproduced using the so-called half-tone process. In this processseveral photographic steps are used to reproduce the graphics image inan array of dots of varying size to reproduce the image on the printingplate. Text information has in the past been hand set, but now may beset by machine under control of electronic devices.

Forming printing plates carrying both graphics and text images mayinvolve several steps, especially when color graphics are to bereproduced. In such a case, several color separation plates must be madefor each color to be printed with the text information being carried onthe plate in which color the text is to be printed. When textinformation is to be located within the field of the graphics image,additional steps are required to form the solid printing text areas forthe plates in that particular color and to remove the graphics imagefrom those same text areas on the remainder of the color separationplates. This of course adds to the number of process steps required toproduce the desired graphics and text images. The steps of forming thetext image to be printed in the graphics field is commonly known asoverburning while the process of removing the graphics image from thosesame text areas in the other color separation plates to be printed isreferred to or is commonly known as stripping.

In overburning, the negatives which form the graphics image and the textimage to be formed in that field are overlayed one on another to formthe desired color separation printing plate. In stripping, othertechniques must be used to remove the graphics information from thosesame text image areas.

The process of forming printing plates containing both graphics and textdata recently has been implemented electronically using essentially thesame methods as were performed manually. Advanced systems however areable to complie data from various input devices that may be used to formboth graphics and text information on a printing plate. These sytemshave their drawbacks in that separate scanning cycles must be performedto form the graphics and text images on a single printing plate and inaddition, complex switching circuits must be constructed to switchbetween text and graphics image formation when text images are to beformed within the field of a graphics image.

The apparatus and method of the present invention overcome the drawbackspresented by the manual and previous electronic systems by providing asystem in which one pass of a beam of radiant energy may form bothgraphics and text images in response to graphics and text data inputthereto. Formation of the graphics and text images may occurindependently of one another so that different imaging schemes may beused to form scaled densities of the graphics images and the binarydensities of the text images.

Formatting of the data in accordance with the invention is such that thegraphics data contains information related to the relative scaleddensities of incremental areas of the graphics image with the remainderof the graphics data for the remainder of the printing plate being anullity to clear the surface of the charged electrophotographic member.The text data is formated such that it does not affect the formation ofthe images carried by the graphics data except in locations where textimages are to be formed.

Formation of text images within the field of graphics images for severaldifferent color separation plates is performed simply by reversing thelogical sense of a control bit of every text data digital word. Thus, toproduce text images of one color such as blue in the field of amulticolor printed graphics image, the same text data may be used forall of the color separation plates with the control bit for the colorseparation plate used to print the color blue being set to one logicalstate and being set to the other logical state for the remainder of thecolor separation plates.

Thus the apparatus and method of the invention provide for imaging of anentire printing plate with graphics and text information in a singlepass of a beam of radiant energy.

The apparatus and method of the invention include an optical system inwhich a beam of radiant energy from a monochromatic source such as alaser is used selectively to discharge and to leave charged incrementalareas of a charged electrophotographic member. Part of the beam is splittherefrom and is used as a reference beam. The remainder of the beam ismodulated to provide a scanning beam or a fine beam comprised ofindividual rays of radiant energy with each ray able to discharge anincremental area of the member. The reference beam and scanning beam orfine beam are aligned vertically with one another with the verticalalignment being used in an optical grating system precisely to determinethe location of the scanning beam along the surface of the member. Afield flattening lens is used in which both the reference and fine beamsare passed through and back again to the member, the field flatteninglens providing the maintenance of a focused image on the surface of themember across every scan line.

A common technique to determine the instantaneous position of thescanning beam along a scan line of the member is to employ an opticalscale or grating composed of alternate bars or spaces of opaque andtransparent, or absorbing and reflecting surfaces or areas. Thesealternating spaces occur at intervals equal to the spacing betweenformable elements on the member to provide electrical signals indicatingthe alignment of the scanning beam with the elements. Light passingthrough or being reflected from such a grating is detected with aphotosensitive device which converts the detected energy into electricalpulses.

Over relatively short scan widths, say 10 inches or so, the problem ofaccurately gathering or collecting light pulses from an optical scaleand directing them to the photosensor is readily accomplished withrelatively simple optics. In much greater scan widths however the costof collecting optics rises exponentially and quickly reaches prohibitivelevels. The apparatus of the invention herein has an active scan lengthof preferably 24 inches. The cost of conventional optics for collectinga reference beam across such a length and establishing a beam feed-backsignal within 1/300 of an inch accuracy is prohibitive.

The concept of using a glass rod or fiber in such a grating collectionsystem is known. The principle used involves having the beam strike therod perpendicular to its cylindrical surface to collect the interceptedenergy in the rod and detect the intercepted energy as it exits the rodat either end thereof. Original results with a short piece of 3/8 inchdiameter glass rod provided poor results, it being believed that most ofthe energy from the beam was transmitted through the diameter of the rodso that the light output at either end of the rod was too low to be ofuse.

The concept of using a hollow metal tube with a high reflective interiorsurface to reduce transmissive losses also was investigated. The tubeused had a very narrow length-wise slit to provide for entrance of theradiant energy reference beam, and a photosensor was mounted at one endof the tube with a mirror located at the other to reinforce thereflected energy levels. It was believed that the reference beam wouldstrike the rear internal surface of the tube and give rise to multiplereflections which would propagate along the tube and result in a usefuloutput level at the end mounted sensor. The optical surface smoothnesson the interior was difficult to control and in turn unsatisfactoryreflections and distributions were obtained. At a consequency thereof,signal levels obtained from the hollow metal tube varied greatly as afunction of the beam position from the sensor along the scan length.Automatic gain and compensation techniques were implemented to modulatethe electronic signal from the sensor, but none of these provedsuccessful. In re-evaluating the glass rod technique, it was believedthat if the transmissive losses of energy could be prevented bycontaining the light within the fiber as within the hollow tube, the rodcollecting scheme might succeed.

A 13/4 inch rod was used because the internal diameter of the existinghollow tube was about 2 inches and this would facilitate concentricmounting of the rod within the tube, and would further minimize energylosses by decreasing the concentric area. Essentially, the glass fiberrod was mounted within the length of the tube. Initial tests met withlittle success until a strip of masking tape was attached longitudinallyof the rod opposite the beam entry point. Increased energy level fromthe non-reflecting surface of the tape was immediately recognized to bethe result of eliminating the air-gap index of refraction (a high losscomponent) while containing and reflecting the entrapped energy in therod. It was quickly determined that highly reflective material such as atypewriter corrector fluid applied to the rod's cylindrical surfacewould be highly efficient in preventing the transmissive loss and aid inproviding good Lambertian distributions. It was later determined that itwas not necessary to coat the entire surface of the cylinder or rod. Anarrow stripe about 1/4 of an inch wide along the rod proved to be morethan adequate. Test results for rods of 0.78 inch, 1.0 inch, 1.5 inchand 1.75 inch diameter indicated that the best results for the barcollector used in the present invention would be obtained with a bardiameter somewhere between 1.5 inch and 1.75 inch.

Two prior art patents which disclose using a bar collector in an opticalscanning or sensing apparatus are U.S. Pat. Nos. 4,040,748 and4,040,745. These patents however do not appear to disclose the use of abar collector over the length provided by the invention herein.

The apparatus and method of the invention further include an electronicsystem that controls the graphics and text imaging process of theinvention. As has been explained, the invention provides for theintermixed formation of graphics and text images on theelectrophotographic member in one sweep or pass of the imaging beam ofradiant energy. The electronics provided are such that formation of thegraphics and text images occur independently of one another, i.e., bothgraphics and text images may be formed at any location of the member.

The electrophotographic member used with the apparatus and method of theinvention proives incremental areas to be imaged that are finer than arepresently available and provides that those elements may be formed at amore rapid rate and with less energy than has previously been providedfor. This electrophotographic coating will be further referred tohereinafter and is the coating described and claimed in U.S. Pat. No.4,025,339.

The apparatus and method of the invention further include a toningsystem which applies minute toning particles to the areas of the latentimage that remain charged. This toning system provides an essentiallyvertical meniscus closely spaced from the horizontal line at whichimaging of the member occurs so that there is a minimal loss of voltage,representing the latent image on the electrophotographic member, fromimaging to toning. Toning systems are known in which toning fluid isapplied to the bottom of a rotating drum carrying theelectrophotographic member wherein the distance from the imaging to thetoning is minimal. In the apparatus of the present invention however, alarge drum is used which rotates relatively slowly so that if a toningsystem were used that is located at the bottom of the drum,substantially all of the latent image would become discharged by thetime the member was rotated to the toning station. Therefore, the toningstation must be located closely spaced from the plane or horizontal lineat which imaging occurs, which requires that toning fluid be applied ina layer which is essentially vertical.

This vertical layer or meniscus is provided by a supply or pressuresystem sealed to the atmosphere, providing toning fluid to escapetherefrom in the form of the layer or meniscus of toning fluid. The rateof escape of the toning fluid is controlled by a valve admittingatmosphere to the otherwise sealed pressure system so that the rate offlow of the toning fluid from the system is substantially equal to themovement of the member past the toning station to provide a verticalmeniscus of toning fluid that is substantially stationary relative tothe member.

SUMMARY OF THE INVENTION

In accordance with the invention a method and apparatus are disclosedthat receive binary digital graphics and text data and in responsethereto form a toned latent image on an electrophotographic member, thetoned image thereafter being fused to the member and the member beingused as a printing plate in an offset lithographic printing press. Thesystem including an optical system, an electronics system and a toningsystem.

The optical system provides a fine beam of up to 22 individual rays ofradiant energy with which to discharge incremental areas of theelectrophotographic member. The optical system further provides fieldflattening to maintain a focused image of the individual rays acrossevery scan line along the original image. An optical scale or gratingsystem comprised of a bar collector is provided that receives areference beam of radiant energy vertically aligned with the fine beam,the bar collector receiving the reference beam across the length ofevery scan line. The bar collector directs the radiant energy from thereference beam to a sensor that provides electrical signals indicatingthe position of the fine beam along the scan line.

The electronics system implements the formation of the text and graphicsimages. The graphics data is used to generate beam modulation signals toform the desired number of individual rays for imaging. The text data isused to modulate the beam modulation signals so that text images may beoverlayed on graphic images or formed outside of the fields of graphicsimages.

A toning system for toning the latent images provides a verticalmeniscus of toning fluid that substantially is stationary relative tothe electrophotographic member as the member is rotated past the toningsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of the apparatus of the inventionillustrating the process of the invention;

FIG. 2 is a side elevational view of the apparatus;

FIG. 3 is a plan view of the apparatus illustrated in FIG. 2 with thecover of the optical system and the drum removed;

FIG. 4 is a schematic diagram of one half of the optical system of theapparatus;

FIG. 5 is a partial schematic diagram of the optical system illustratedin FIG. 4 taken along the lines 5--5 and in the direction indicated;

FIG. 6 is a partial schematic diagram of the optical system illustratedin FIG. 4 taken along the lines 6--6 and in the direction indicated;

FIG. 7 is a partial schematic diagram of the optical system illustratedin FIG. 4 taken generally along the lines 7--7 and in the directionshown;

FIG. 8 is a representation of the elements of a field flattening lenssystem;

FIG. 9 is a schematic diagram of the optical scale or grating systemincluding a bar collector illustrated in FIG. 4 taken generally alongthe line 9--9 and in the direction indicated;

FIG. 10 is a top view of the bar collector illustrated in FIG. 9arranged with a sensor;

FIG. 11 is a chart of a field of graphics image areas and text pixels;

FIG. 12 is a chart of a field of graphics pixels;

FIG. 13 is a chart of a field of text pixels overlaid with four graphicspixels;

FIG. 14 is a schematic block diagram of the electronic and opticalsystems of the apparatus;

FIG. 15 is a schematic block diagram of the pattern generatorsillustrated in FIG. 14;

FIG. 16 is a schematic block diatram of the beam logic circuitillustrated in FIG. 14;

FIG. 17 is a chart illustrating the groups of individual rays that arecontrolled by individual bits of text data words;

FIG. 18 is a schematic block diagram of the multiplex and gatingcircuits of FIG. 16;

FIG. 19 is a schematic block diagram of the toning system of theapparatus;

FIG. 20 is a perspective view of the toning station and drum;

FIG. 21 is a perspective view of a shoe of the toning system illustratedin FIG. 19;

FIG. 22 is a sectional view of a charging station and the shoeillustrated in FIG. 21 illustrating the relationship of the chargingstation and shoe to the drum; and

FIG. 23 is an exploded view of a portion of the interface between thedrum and the shoe illustrating the relative positions of theelectrophotographic member, the toning fluid and the shoe.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment, the imaging device receives digital datarepresenting the graphics and text images to be printed or otherwisereproduced. This digital data is received from a compiling system whichobtains raw data from such as an optical scanning system, text inputstations, etc., and compiles or formats the data representing thegraphics and text materials into a form which may be used by the imagingdevice of the invention herein. The data received by the imaging devicealso may be generated or synthesized by a computer or by other means andmay be presented to the imaging device from a memory in which it hasbeen stored or it may be presented on line as it is generated orsynthesized if the generation of sythesization rate is equal to or lessthan the imaging rate of an imaging device herein.

The output of the imaging device herein is an electrophotographic membercarrying a toned latent image of charged and discharged incrementalareas formed in response to the digital data. The toned memberthereafter may be fused and processed for use as a printing plate in anoffset lithographic printing press with the toned areas carrying ink toa receptor to form the tonal graphics and text images. If color printingis desired, several electrophotographic members carrying toned latentimages are formed, one for each color that is desired to be printed.Each member carries a toned latent image for each of what are commonlyknown as color separations.

The imaging device or imager used in the preferred embodiment of thisinvention uses a laser beam to image an electrophotographic member thatincludes a photoconductive coating that previously has been charged. Themember is carried on a rotary drum, is toned on the drum and thereaftermay be used to transfer the toned image or to serve as a medium forprojection or printing of the image. In the case of printing, the tonedimage is used to carry ink in a printing press, the member having beentreated to achieve hydrophilic and hydrophobic areas to enable offsetlithographic use of the member as a printing plate.

The preferred use of the imaged member herein is as a printing plate andthe member has an electrophotoconductive imagable coating that ispreferably the receptor of the laser beams which comprise the outputfrom the appartus of the invention. Such coating is that which isdescribed and claimed in U.S. Pat. No. 4,025,339, incorporated herein byreference.

The apparatus and method of the invention may best be understood byconsidering that the binary digital data input to the apparatus is usedbinarily to modulate a beam of radiant energy from a laser selectivelyto discharge and leave charged incremental areas of the chargedelectrophotographic member. Thereafter, the selectively charged anddischarged pattern or image carried on the member is toned and outputfrom the apparatus.

The electrophotographic member is carried on the outer circumference ofa drum which is rotated around its longitudinal axis. Charging, imagingand toning of the member occurs sequentially at adjacent stations as themember is moved past the stations by the rotating drum. Charging of theelectrophotographic member may be by any means desired and in thepreferred embodiment occurs by placing adjacent the outer circumferenceof the drum a corona wire having a high voltage applied thereto. Toningof the imaged member occurs by applying to the member a quantity ofcarrier fluid containing toner particles. The charging and toning occursat stations respectively above and below an imaging plane. Imaging ofthe charged electrophotographic member occurs by passing a fine beam ofradiant energy from a laser across the surface of the member in imagelines that are parallel to the longituinal axis of the drum and lie inthe imaging plane. Imaging of the entire surface of the charged memberoccurs in sequential image lines as the member is moved by the drum pastthe imaging plane.

The digital input to the imaging apparatus is in the form of twochannels of graphics data and one channel of text data. Each digitalword of the graphics data is used to form one graphics picture elementor graphics pixel on the coating of the electrophotographic member.Every imaging line is comprised of two scan lines of graphics pixelswith each channel of graphics data respectively controlling theformation of graphics pixels in one scan line.

The text data controls the formation of text pixels across the width ofthe image line (comprised of two scan lines) and therefore only onechannel of text data is required. Every word of the text data iscomprised of 8-bits of information with the least significant six bitseach controlling the binary density of a text pixel, the next leastsignificant bit serving as a control bit, and the most significant bitnot being used.

The graphics data and text data are formated such that they each mayform respective graphics or text images across the entire area of theelectrophotographic member. The electronics of the invention herein usesboth text and graphics data to form one channel of laser modulationsignals. Further, in the imaging apparatus herein, the informationcarried by the text data is used to gate the formation of the individualrays of the fine beam of radiant energy, each of which rays is used todischarge an incremental area on the charged electrophotographic member.Simply stated, the text data is used to gate or modulate the formationof graphics pixels in response to the graphics data: if the text data isa nullity and no text images are to be formed on the member, theinformation carried by the graphics data will form the graphics imagerepresented thereby and discharge the remainder of the member.

Where the text data contains information representing a text image to beformed on the member, the text data may either inhibit or enable theformation of individual rays of the fine beam depending on the logicalstate of the control bit included in each word of text data. When thetext data inhibits the formation of individual rays of the fine beam, atext image is formed on the member that will be toned and in theprinting plate will carry ink to the receptor to print a solid image.This is the case where printed, such as black, text is desired on anybackground. When the text data enables formation of individual rays ofthe fine beam, text pixels are discharged on the member with thedischarged areas of the member forming areas of the printing plate whichdo not print on the receptor or which remain clear. This is the casewhere clear or non-printed text is desired within a graphics image.

In the preferred embodiment of the invention, the text pixels are ninetimes more numerous than the graphics pixels, i.e., for every graphicspixel there are nine text pixels which may be discharged or leftcharged. The resolution provided by the text pixels is not, however,nine times the resolution provided by the graphics pixels because ofoverlap of the text pixels. Of course, it will be understood that theelectrophotographic member is not physically divided into picture areasor pixels of any type; there are no scan lines or image lines scribed onthe member but that these terms are used only to describe the operationof the imaging apparatus and method.

Referring now to FIG. 1 of the drawing, the apparatus of the inventionillustrated schematically is indicated generally by the referencecharacter 30. Two channels of graphics data are received by theapparatus respectively at channel A and channel B graphics data buffers32 and 34. Text data is received into text data buffer 36. The graphicsdata contained in data buffers 32 and 34 individually are applied topattern generators 38 and 40 over leads 42 and 44. In pattern generators38 and 40, the density information carried by the digital words of thegraphics data are converted into patterns of elements which are to beformed in graphics pixels on the member, the pixel patterns representingthe densities indicated by the graphics data.

The pattern information produced by pattern generators 38 and 40 then isapplied to beam logic 46 on leads 48 and 50 together with the text datafrom text data buffer 36 on lead 54. In beam logic 46, the text data isused to modulate the pattern information from pattern generators 38 and40. The output of beam logic 46 is applied to acousto-optic deflector 54and is the ray data which controls the formation of individual rays inthe fine beam. The output of beam logic 46 is carried to theacousto-optic deflector 54 on lead 56. A radiant energy source 58produces a beam of radiant energy 60 that is substantially at one wavelength and that is directed to acousto-optic deflector 54. Radiantenergy source 58, in the preferred embodiment, is a laser with the wavelength of the beam of radiant energy 60 being chosen advantageously todischarge areas of the electrophotographic member. Acousto-opticdeflector 54 modulates the beam of radiant energy 60 to provide a finebeam 62 of radiant energy comprised of a plurality of individual raysand in some cases as little as a single ray.

The fine beam 62 is directed onto an electrophotographic member 64carried on a drum 66 rotating in the direction indicated by arrow 68.The thickness of member 64 is exagerated in FIG. 1 so that member 64 mayeasily be seen on the circumference of drum 66. Charging of member 64occurs at charging station 70 prior to the time at which fine beam 62 isapplied to member 64 and toning of member 64 occurs at station 72 afterimaging by fine beam 62.

While the preferred purpose of the invention is to make offsetlithographic plates by electrostatic techniques described herein, anyuse of an electrophotographic member will find advantages where a memberhas been imaged according to the invention.

In forming several different color separation plates, it may be desiredto form text images of a single color (for example blue text) in a fieldof a graphics image or otherwise. Thus in the blue printing separationplate, the text image must be formed solid. On the other colorseparation plates that same area must be cleared so that only the colorblue will be printed on the receptor. By selectively using the solidforming and clearing capabilities of the text data, one may form thesolid printing blue text image in the field of graphics or otherwise asmay be desired.

Turning now to FIGS. 2 and 3, the preferred embodiment of the apparatusof the invention is illustrated including some of the cabinetry providedtherewith. The apparatus 30 includes an optical cabinet 80 whichencloses a left-hand optical system 82 and a right-hand optical system84. Drum 66 extends the width of both the left-hand and right-handoptical systems 82 and 84 so that an electrophotographic member carriedthereon may be simultaneously and separately imaged by the respectiveoptical systems. Drum 66 is supported at each end by supports 86 and 88and is rotationally driven by motor 90. In FIG. 2, the drum is shownenclosed by a housing 92 that protects an electrophotographic membercarried on drum 66 from ambient light. Optical cabinet 80 and housing 92adjoin each other, there being only a small slit opening between themthrough which the fine beam passes on its way to the chargedelectrophotographic member.

The electrophotographic member is held on drum 66 by a magnetic chuckthat is formed of magnetic strips extending the length of drum 66 at thecircumference thereof. The magnetic field produced by these magneticstrips is strong enough so that an electrophotographic member having asubstrate of such as stainless steel will be securely held on the drum.

Alternatively, the member could be maintained in fixed relationship onthe drum 66 by other hold-down systems such as vacuum systems, clamps,springs, etc.

In the preferred embodiment, the drum circumference is 1250 millimeterswhile the drum length is 1,100 millimeters. The drum is continuouslyrotated at a speed of 0.125 RPM which corresponds to 180 revolutions perday or 8 minutes per revolution. This provides a drum speed of 2.6millimeters per second.

The center line of the charging station 70 is arranged to be 25 degreesabove the image plane, while the center line of the toning station 72 isarranged to be 30 degrees below the imaging plane. This is best seen inFIG. 22.

The maximum size electrophotographic member which may be carried by thedrum 66 is a member which is 1,040 millimeters by 1,040 millimeters andthe area of the member which may be imaged by each of the left and righthand optical systems is about 50 centimeters axial of the drum by 70centimeters circumferential of the drum or an area which is about 20×28inches.

A cabinet 94 is provided for the toning system toning tanks and pumpswith the hydraulic and pneumatic connections between cabinet 94 andtoning station 72 not being shown in FIGS. 2 and 3 for clarity of thosefigures. Mounted on the exterior of cabinet 80 are two laser sources 96and 98, which provide the radiant energy respectively to the left-handand right-hand optical systems 82 and 84. The entire apparatus 30 issupported by a frame 100 having the general configuration of a table.Auxiliary equipment for operating the apparatus 30 such as powersupplies for the laser sources 96 and 98, servo or control electronicsfor the motor 90 and auxiliary tanks for the toning system may bemounted under frame 100, and are not shown in FIG. 2 for clarity or thefigures.

As may be seen in FIG. 3, the left-hand and right-hand optical systems82 and 84 are mirror images of one another.

Referring also to FIGS. 4, 5, 6 and 7, laser source 96 provides a beamof radiant energy 60 to spatial filter 110 that provides what may betermed a pinhole aperture to obtain a desired cross-sectional size ofthe beam. The beam 60 is transmitted through spatial filter 110 tofolding mirror 112 which deflects beam 60 to beam splitter 114.

A portion of beam 60 is transmitted through beam splitter 114 and formsa reference beam 118 which is deflected by folding mirrors 120 and 122to a spot forming lens 124. The portion of beam 60 that is deflected bybeam splitter 114 is directed to acousto-optic deflector 54 that formsfrom beam 60 the individual rays which have been refered to as the finebeam 62. Fine beam 62 exits acousto-optic deflector 54 and passesthrough spot forming lens 126 and over folding mirror 128. Referencebeam 118 passes through spot forming lens 124 and is deflected byfolding mirror 128. After fine beam 62 passes over folding mirror 128,fine beam 62 and reference beam 118 are vertically aligned with oneanother through the remainder of the optical path.

Referring to FIG. 5, reference beam 118 as it is transmitted throughbeam splitter 114 is represented by crossed lines indicating the lightin reference beam 118 is exiting the drawing figure. Folding mirror 128is shown in FIG. 5 located below fine beam 62 after fine beam 62 passesthrough spot forming lens 126. The dotted circle at the center offolding mirror 128 represents that reference beam 118 is directed intodrawing FIG. 5. Fine beam 62 and reference beam 118 then are deflectedby folding mirror 130 with the crossed lines on folding mirror 130indicating that the light is exiting from the drawing figure.

The dotted circles on folding mirror 130 in FIG. 6 indicate that thelight is entering the drawing figure.

Fine beam 62 and reference beam 118 are then passed through a relay lens132 to a folding mirror 134. Again the crossed lines on folding mirror134 in FIG. 6 represent that the beams are exiting the drawing figure.In FIG. 7, beams 62 and 118 are deflected by folding mirror 134 throughan fθ lens system 136 to a galvanometer mirror 138. Galvanometer mirror138 is rotatably oscillated in the directions indicated by arrow 142 anddirects fine beam 62 back through the fθ lens system 136 through anaperture 144 extending through the front plate 146 of cabinet 80 andthen onto the charged electrophotographic member 64. Reference beam 118is deflected by galvanometer mirror 138 back through fθ lens system 136and onto a folding mirror 148 to an optical scale or grating system 150.

It will be noted that the deflection of fine beam 62 and reference beam118 in horizontal directions by galvanometer mirror 138 does not disturbthe vertical alignment of these two beams so that the position ofreference beam 118 may be sensed by the optical scale or grating systemprecisely to locate the position of fine beam 62 as it is used to imageor write the images on the electrophotographic member 64. Galvanometermirror 138 deflects fine beam 62 through a scan line 152 illustrated inFIG. 6 and deflects reference beam 118 along a scan line 154 lying ondeflecting mirror 148. The extent to which the galvanometer mirrordeflects fine beam 62 and reference beam 118 are represented in FIG. 4by dashed lines 156.

In FIGS. 6 and 7, it will be seen that fine beam 62 and reference beam118 are located below the imaging plane defined by fine beam 62 as itpasses through aperture 144 and is directed onto electrophotographicmember 64. The fθ lens system 136 provides field flattening for bothfine beam 62 and reference beam 118 so that they may be maintained infocus respectively across the surface of the electrophotographic member64 and across the surface of the optical scale or grating system 150.

The spatial filter, folding mirrors, beam splitters, spot forminglenses, relay lens and galvanometer mirror are all common opticalelements which readily may be constructed and arranged in a system ashas been described, as may be desired.

In the preferred embodiment the spot forming lenses have a focal lengthof 26 millimeters, the relay lens has a focal length of 200 millimetersand the fθ system has a focal length 870 millimeters. The distancebetween the spot forming lens and the relay lens is 559.2 millimeterswhile the distance between the relay lens and the fθ lens is 1,190millimeters. The distance from the fθ system to the focal plane at theelectrophotographic member 64 and the optical scale system 150 is 870millimeters.

The fθ lens system 136 is illustrated in FIG. 8 and comprises elementsL1 through L4 having surfaces defined by radii R1 through R8 as shown.

The lens of FIG. 8 comprises from the object end a first, negativecomponent L1 having a concave object side surface a second, positivecomponent L2 having a concave object side surface; a third positivecomponent L3 having a flat object side surface; and a fourth positivecomponent L4 having a flat object side surface and a convex image sidesurface.

The lens of FIG. 8 is defined substantially by the data of Table I, asscaled to a focal length of 870 millimeters;

    ______________________________________                                                         Axial Distance                                               LENS  Radius     Between Surfaces (mm)                                                                           N.sub.d                                                                            V.sub.d                               ______________________________________                                            R1    -161.744                                                            L1                   15.00           1.617                                                                              36.6                                    R2    ∞    6.97                                                         R3    -216.311                                                            L2                   28.871          1.523                                                                              58.6                                    R4    -213.119                                                                                 0.20                                                         R5    -2575.204                                                           L3                   18.06           1.523                                                                              58.6                                    R6    -264.288                                                                                 0.20                                                         R7    ∞                                                             L4                   13.00           1.523                                                                              58.6                                    R8    -265.847                                                            ______________________________________                                    

The lens disclosed may of course be scaled otherwise as it is desired.

The acousto-optic deflector 54 is capable of separating beam 60 into asmany as 22 individual rays or beamlets which form fine beam 62. These 22rays are indicated in FIGS. 12 and 13. In the preferred embodiment asmany as 22 individual radio frequency signals may be applied toacousto-optic deflector 54 on lead 56 (see FIG. 1) to deflect the 22individual rays, each radio frequency signal being capable of deflectingone individual ray. Acousto-optical deflector 54 is constructed andarranged so that the individual rays that are deflected from beam 60 arealigned vertically in fine beam 62 and so that the focused images formedon the electro-photographic member 64 are arranged adjacent and spacedequidistant from one another. Thus a radio frequency signal of the firstfrequency will form one individual ray while the next radio frequencysignal will form an adjacent ray and so on. In the preferred embodimentacousto-optic deflector 54 is capable of deflecting 22 individual raysand although deflector 54 operates on the principle of acousticallydeflecting the individual rays other deflector apparatus may be used inplace thereof.

In FIGS. 9 and 10, the optical scale or grating system 150 comprises agrating 160, a bar collector 162 carrying a narrow stripe of reflectivematerial 164 on the outer surface thereof and a sensor 166 such as aphotomultiplier tube. The optical scale or grating system 150 extendsthe entire length of the scan lines across which fine beam 62 andreference beam 118 are deflected, see FIG. 4, as do grating 160 and barcollector 162.

Grating 160 is an elongate transparent member carrying alternatingopaque and transparent lines or spaces having a frequency related to thefrequency of the rows in an imaging line. Grating 160 is arranged sothat reference beam 118 is deflected across the opaque or transparentareas or lines on every imaging line.

Bar collector 162 is an elongate cylindrical member which extends thelength of grating 160 and is arranged relative to grating 160 so thatwhen reference beam 118 passes through grating 160, reference beam 118passes through the diameter of bar collector 162 to strike transparentmaterial 164. When reference beam 118 strikes reflective material 164, alambertion distribution of the scattering or reflecting light occurs inthe bar collector 162 and the light so entering bar collector 162remains therein and is transmitted to the end of bar collector 162 whereit is sensed by sensor 166. As shown in FIG. 10, the end of bar collect162 opposite sensor 166 carries a mirror 168 thereon or has a mirroredsurface to reflect light along the length of the collector to the sensor166. Sensor 166 provides an analog electrical signal on leads 170 thatindicates reference beam 118 entering the bar collector 162.

In the preferred embodiment bar collector 162 has a diameter of 1.75inches and is made of such as acrylic materials although the materialknown under the trademark of Lucite has provided good results. Thenarrow stripe of reflective material 164 may be any highly reflectivematerial and in the preferred embodiment a typewriter correction fluidis used. The length of the bar collector 162 is about 24 inches toprovide the desired 20 inch imaging line plus sufficient length forhousekeeping and related needs.

In evaluating the glass fiber technique used herein for the barcollector 162 it was discovered that by placing a strip of masking tapealong the length of bar collector 162 opposite the point of entry ofreference beam 118 that a significant increase in the energy transmittedby bar collector 162 to sensor 166 was obtained. The increased energylevel from the nonreflecting surface of the tape was immediatelyrecognized to be the result of eliminating twice the area-gap index ofrefraction (a high loss component) while containing and rereflecting thetrapped energy beam. It was quickly determined that a highly reflectivematerial such as typewriter correction fluid applied to the rod'scylindrical surface would be highly efficient in preventing thetransmissive loss and aid in providing good lambertion distribution ofreference beam 118 striking the same. Further investigation showed thatit was necessary to coat only a stripe about 1/4 of an inch wide alongthe length of the rod to provide more than adequate energy for thesensor 166. Best results for 24 inch long rods indicated that the bestenergy response was obtained by using a rod diameter of from 1.5 inchesto 1.75 inches.

In the preferred embodiment the grating 160 has a three hundred line perinch optical scale to provide the signals from sensor 166 to locate theposition of fine beam 60 along electrophotographic member 64.

It is important that the sensor 166 not look at the entire cross-sectionof the end of the collector tube 162, but only at a smaller areacentered around the longitudinal axis of a bar collector 162. It also isimportant that only the single narrow stripe of reflective material 164be on the circumference of the bar and the remainder of thecircumference of the bar be clean to maximize the internal reflection oflight in the bar. The leads 170 from the sensor 166 in the preferredembodiment are connected to an automatic gain control amplifier tosmooth out the signal from the bar collector 162 in response to beam 118entering the collector at different distances from the sensor. In thepreferred embodiment the signal from the automatic amplifier is used ina phase-locked-loop circuit to provide the desired signals indicatingthe location of a fine beam 62 along the imaging lines on the member 64.

It is important that the reference beam 118 present a focused imageacross the entire length of grating 160 so that the signals providedfrom sensor 166 will be well defined. If the reference beam presentsfocused images that are off the plane of grating 160, the edges of thepulses generated from sensor 166 will not be well defined and thelocation of fine beam 62 along the imaging lines will not be precise.

As has been stated digital data that is input to the apparatus is in theform of graphics data and text data. The graphics data is used toreproduce graphic images on the electrophotographic member 64 with oneblack and white image or one color separation image being formed on eachmember.

The graphics data is in the form of binary digital words with the valueof each word representing a scaled areal density to be formed on animaging area on the member. Each word is used to select a pattern ofelements from a memory or other storage device which represents thescaled (gray scale) density equal to the value of the graphics digitalword.

The patterns selected from the memory are formed on the member bydischarging and leaving charged elements in an imaging area. Theelements are arranged equispaced across the surface of the member andare arranged in rows and columns. Selective elements in the imagingareas are used to form the patterns and in the preferred embodiments theelements are grouped together in irregular hexagonal picture elements orpixels. It should be remembered that the configuration of the pixels isa choice of the designer, the imaging areas in which the configurationsmay be formed being of a predetermined number of rows and of apredetermined number of columns. One pattern then may be formed in onepixel

The columns at which the elements are located are defined by thehorizontal lines across the member that would be described by theindividual rays or beamlets of the fine beam 62 as they are passedacross an imaging line. The rows of the imaging lines perpendicular tothe columns and are defined by the sample clock signals produced fromthe grating system 150.

The imaging lines are comprised of two scan lines of graphics pixelswith each scan line of graphics pixels being controlled by one graphicsdata channel. Thus channel A graphics data controls the graphics pixelsto be formed in scan line A, and the graphics data in channel B controlsthe graphics pixels to be formed in scan line B.

It bears repeating that if the text data contains no information to beformed on the electrophotographic member 64, the graphics data isformated so that the graphics image or images contained therein will beformed on the member 64 while the remainder of the surface of member 64will be discharged. Thus, the printing plate formed by such graphics andtext data will print on the receptor only the graphics image or imagesand leave a clear background.

The text data is used to reproduce text images and line graphics such ascharts and graphs on member 64. While the graphics data provides for thescaled density of the imaging areas to be formed on member 64, the textdata is used to provide binary imaging or image areas of the member 64which in the preferred embodiment are the same as text pixels.

In the preferred embodiment the text pixels have a definite relationshipto the graphics pixels.

In every imaging line the text pixels are aligned six abreast along eachrow and are two rows wide. Specifically, what may be called the firsttext pixel or scan line covers the area defined by the first fourcolumns of individual rays by two rows deep. The next text pixel isthree columns wide by the same two rows deep. The next two text pixelsare each four columns wide and the same two rows deep. The next textpixel is three columns wide and the same two rows deep, and the lasttext pixel is four columns wide by the same two rows deep. Thus, it maybe said that the text pixels are arranged across the imaging line atevery two rows. Every word of the text data represents the binary imageto be formed in the text pixels formed along the same two rows of theimage line.

For each of the six text pixels in those two rows, there are fourpossible states or conditions. The first two states are defined as beingthe normal mode, the first state or condition or which will inhibit theformation of rays of fine beam 62 to discharge areas of the member 62.These charged areas will form solid printing areas that will print suchas black ink on a white background. The second state or condition willenable the formation of individual rays of fine beam 62 as determined bythe graphics data for that row. The last two states are defined as beingthe reverse mode. The first condition of the reverse mode or third statecauses a formation of rays of fine beam 62 to discharge areas of themember 64. These discharged areas will then form text images in areasotherwise formed of graphics images to provide printing plates whichprint clear text in graphics images. The second condition of the reversemode or fourth state enables the formation of rays under control of thegraphics data.

These four states are formed of the binary combination of a control bitand one data bit of every word of the text data. Thus, as will beexplained hereinafter, one data bit and one control bit of every wordcontrols inhibiting of the formation of rays, enabling of formation ofrays by the graphics data or causes the formation of rays in every textpixel.

If the graphics data is a nullity and is used only to clear the entireplate, then the information contained in the text data will be able toform text images only by inhibiting the formation of rays to leavecharged areas which will print solid on the receptor. This is the firststate or condition under the normal mode. It will be noted that textimages will not be able to be formed by the first condition of thereverse mode or the third state which causes the formation of raysbecause the graphics data is clearing the plate and there will be nobackground against which to form the clear text images.

If the graphics data is full density for the entire plate, no rays willbe formed anywhere across the plate by the graphics data. In such acase, the only text images which may be formed are under the reversemode first condition or third state which which causes the formation ofthe rays to discharge areas in an undischarged field to print clear in afield of solid printing area. It will be noted that in such a case thefirst state or condition of the normal mode has no effect to create orform a text image by inhibiting the formation of rays because there areno rays being formed by the graphics data.

Thus, the relationship between the graphics and text data may bedescribed as one where the graphics data is able to form graphics imagesacross the entire imaging area of the member 64 and depending upon thegraphics images so formed the text data may form text images. Moreover,the graphics data and the text data contain enough information to imagethe entire imaging area of member 64 with the formation of patterns inthe graphics pixels and the formation of the text pixels beingindependent of one another. Imaging the graphics and text in this matterhas advantages in that different imaging schemes for the graphics may beimplemented without interfering between the relationship between thegraphics and text imaging.

Referring now to FIGS. 11, 12 and 13, there is illustrated in FIG. 11 achart of three imaging lines which are formed on the electrophotographicmember 64. Imaging lines 1 and 2 illustrate the formation of graphicspixels while image line 3 illustrates the formation of text pixels. Allthree image lines represent the extent of imaging that may be performedby each of the left- and right-hand optical systems 82 and 84 on itsrespective one half of the member 64.

Image lines 1 and 2 each comprise an A-channel scan line and a B-channelscan line, there being three thousand (3,000) image positions in each ofthe A-channel and B-channel scan lines with the imaging positions in theB-channel scan lines being offset relative to the imaging positions inthe A-channel scan lines. Thus, in each of image lines 1 and 2, thereare 6,000 graphics pixels which may be formed.

It will be remembered that the imagable area across the width of themember 64 is about 40 inches so that the left and right-hand opticalsystems 82 and 84 each image a width of about 20 inches. Dividing 20inches into the 3,000 image positions of each channel in an image lineresults in a frequency of about 150 positions per inch or about 6 imagepositions or graphics pixels per millimeter. This provides a 150 lineper inch resolution commonly desired in the printing industry.

Referring now to FIG. 12, there is depicted a field of graphics pixelsthat may be presumed to be laid out on the surface of theelectrophotographic member 64. The pixels are irregular hexagonal areasdesignated GP1, GP2, GP3, GP4, GP5, GP6 and GP7 inclusive and are partsof an overall pattern of hexagons which cover the surface of member 64.Obviously, the defining lines illustrated in FIGS. 11, 12 and 13 areimaginary and merely represent a theoretical geometric pattern which forconvenience describes the manner in which the imaging is effected.

The individual rays of fine beam 62 are going to remove charge from theareas of the charged member to form elements of the graphics pixels. Thepossibility for removal is represented in this case by elements ofdischarge which are generally circular and which account for the entireinterior of each graphics pixel. The graphics pixels according to theinvention are arranged in interleaved columns so that the field ofpixels may be considered to occupy all of the area. Graphics pixels GP1,GP2 and GP3 are shown with their flat sides respectively in common at200 and 202 while the flat sides of graphics pixels GP4 and GP5 are incommon at 204. The adjoining pixels to the left and to the right ofthese pixels are also arranged in this way. The graphics pixels inadjacent scan lines are interleaved or staggered relative to oneanother; hence, pixels GP4 and GP5 have their top apices at the locationof the common flat sides 200 and 202 of pixels GP1, GP2 and GP3 asindicated in FIG. 11 for adjoining scan lines.

Graphics pixels GP1, GP2, GP4 and GP5 have centering points laid out inthem that are numbered and that can be seen to be formed at thejunctures of rows and columns that are marked above and to the left ofthe field of pixels. The columns are defined as imaginary linesdescribed by each of the individual rays of fine beam 62 as fine beam 62is swept across the image line. The rows are defined along the imageline by clock pulses from the optical grating system 150 and occur atequidistant intervals along every image line.

In the preferred embodiment, the image positions illustrated in FIG. 11are defined as having six rows numbered 0-5 and 11 columns. Scan line Ais formed of columns 1-11 while scan line B is formed of columns 12through 22, the column numbers corresponding to the number of theindividual rays. While the graphic pixels GP1 through GP5 in thepreferred embodiment have been defined as irregular hexagons having thenumber of elements illustrated, the graphics pixels may be defined ashaving any geometric configuration desired which fits the limitations ofthe six rows and eleven columns. As will be described more fullyhereinafter concerning the electronics, the limitations of six rows andeleven columns is purely one of electronics such that by modifying theelectronics any number of columns and rows may be defined to be animaged area and in turn any geometric configuration desired may beformed therein.

In the preferred embodiment there are 24 centering points for theelements in each graphics pixel and these are arranged in elevenhorizontal columns and six vertical rows. The columns are all confinedwithin each graphics pixel between its top and bottom apices. Allgraphics pixels are considered to be oriented exactly the same withtheir long flat surfaces left and right and apices top and bottom. Therows are arranged somewhat differently. Five of the rows will havecentering points that are within the confines of the graphics pixelbetween left and right flat sides, while the sixth row image will neverhave centering points located thereon and is coincident with the leftand right flat sides of the graphics pixels. This is a spacing expedientto be explained later.

The centering points which have been described are the centers of thecircular dischargable or formable elements such as 210 which are goingto be discharged by the individual rays. As seen, the circular element210, which is the same as all others, is large enough so that inaddition to covering a certain area within its graphics pixel itoverlaps into the adjoining pixel. Thus, the circular element 210 notonly discharges the area within the graphics pixel GP3 that itencompasses but also discharges a cordal slice or segment in each of thegraphics pixels GP6 and GP7 as indicated at 212 and 214, respectively.

If we drew a line between each of the centering points vertically anddiagonally, we would see the overall patterns of general hexagonal areawhich can be seen in the pixels GP1, GP2, GP4, GP5 and of course thesehexagons have the appearance that they are made up of a plurality ofequilateral triangles. Thus, the circular discharge elements such as 210will discharge the area around its centering point comprised of the sixequilateral triangles surrounding that centering point plus six morecordal segments beyond that hexagon defined by those triangles. Andsince every other circular element will also discharge thephotoconductive surface of the electrophotographic member in the sameway, the discharged circular elements that are side by side alwaysoverlap.

Graphics pixel GP3 has six of the top circular elements shown in outlineat 216 and there, overlapped areas are readily ascertained. In addition,there can be seen the 8 overlapped cordal segments of discharge areathat protrude into adjoining pixels including the pixels GP2 and GP7.For explanatory purposes, the total discharged area of any graphicspixel can ba approximated by the triangles which are included in thecircular elements discharged. The more circular elements of discharge ina given graphics pixel, the better the approximation because of theoverlap within the graphics pixel. In the circular element 210 theequilateral triangles are identified as TR1 to TR6 inclusive.

It is illustrated in each of graphics pixels GP1 and GP4 that in thehorizontal columns there is only one centering point in each of columns1, 11, 12, and 22; two centering points in each of columns2,4,6,8,10,13, 15, 17, 19 and 21; and three points in each of columns,3, 5, 7, 9,14, 16, 18 and 20. These conditions are requirements of theelectronics and may be altered by altering the electronics as isdesired. These conditions must be met during the laying down of thedischarge elements.

The fine beam 62 which makes one pass to provide the horizontal columninformation for generation of the centering points for the graphicspixels that are being described in an image line, will be composed of amaximum of 22 individual rays passing over the image line. It is assumedthat all rays will be used for the graphics pixels in an image line butthe maximum number of rays or beamlets that will be operating at anygiven time for the configuration illustrated in FIG. 12 will be 9,because as is illustrated in FIG. 12 there are no more than 9 centeringpoints along any one row. This is shown in graphics pixels GP2 and GP4,at scan line A rows 0 and 1 and scan line B rows 4 and 5. Along scanline A row 0 and scan line B row 4, centering points 1, 2, 3 and 4 ofgraphics pixel GP2 are defined, while centering points 16, 17, 18, 19and 20 of graphics pixel GP4 are defined. Of course, the minimum numberof rays or beamlets operating will be zero.

Summarizing then, the horizontal columns of centering points arecontrolled by the number of individual rays in a fine beam 62. The rowsare controlled by the information that is obtained from the opticalgrating system 150. The row information is used in the beam logicelectronics to discharge the desired elements as will be describedhereinafter. The patterns that are imaged in the graphics pixels inresponse to the density values indicated by the digital words of thegraphics data may be of any configuration desired to represent theequivalent density and in the preferred embodiment, there is onepredetermined pattern which is to be formed in the graphics pixel forevery density value indicated by the graphics data.

In the preferred embodiment the distance between the center lines ofscan line A and scan line B is 169.3 microns while the distance betweenthe flat sides of each graphics pixel is 171.7 microns. The diameter ofeach of the discharged elements is 35 microns with all of these valuesbeing based upon a 150 line per inch resolution.

It will be noted that as there are 24 individual elements in eachgraphics pixel that may be either charged or discharged. This results ina total of 2²⁴ or approximately 16 million combinations of dischargeelements which are available to image the desired density patterns.Thus, even if the graphics data may only represent 256 steps of densitywith 8 bits of information per graphics digital word, each step of the256 step gray scale may be represented by a plurality of the 16 millionavailable patterns which have density values equal to or approximatelyequal thereto.

The text pixels which are formed in response to the text data areillustrated in FIGS. 11 and 13. In FIG. 11, image line 3 has six scanlines of text pixels. The text pixels are arranged 3 wide for everygraphics data scan line and are two rows deep. The arrangement of thetext pixels relative to the graphics pixels and the rows and columnsdescribed hereinable is illustrated in FIG. 13.

The text pixels are arranged slightly shifted in relation to thegraphics pixels, and there are about 9 text pixels per graphics pixelsor graphics image area. Referring to FIG. 11, along one image line thereare 9,002 rows of text pixels with six text pixels per row. The 9,002rows of text pixels results by multiplying the 3,000 graphics pixel perscan line for each of the left- and right-hand optical systems 82 and 84by 3 rows of text pixels per graphics pixel plus two additional rows oftext pixels required to cover the area uncovered by the shift inposition of the channel A and channel B graphics pixels.

The relationship of the text pixels to the graphics pixels in the Achannel scan line and B channel scan line is illustrated in both FIGS.11 and 13. The relationship of the text pixels to the columns defined bythe individual rays is illustrated in FIG. 13.

FIG. 13 illustrates text pixels TP1-TP48 arranged along one image lineand illustrates in dashed lines the relationship thereto of graphicspixels GP1, GP2, GP4 and GP5. The electronics of the digital platemakersystem are arranged so that each word of the text data received therebyoperates on one row of text pixels that are six abreast. Thus,successive words of the text data operate on respective text pixelsTP1-TP6, TP7-TP12, TP13-through TP18, etc.

Each text pixel is defined as being that area which encloses a certainnumber of discharge elements which are formable by certain rays of thefine beam 62 across two successive graphics channels. By reference toFIG. 12 it will be seen that the rows indicated at the top of FIG. 13correspond to the rows indicated at the top of FIG. 12. The areasenclosed by the text pixels with reference to the formable dischargeelements are illustrated in FIG. 13 where for example, text pixel TP-31is formed of the area including the elements formed by rays 1, 2, 3 and4 in the graphics A channel, rows 3 and 4. Text pixel TP-32 is formed ofthe area including the elements formed by rays 5, 6 and 7 in the samerows 3 and 4. Text pixel TP-33 is formed of the area including theelements formed by rays 8, 9, 10 and 11 in the same rows 3 and 4. Textpixel TP-34 is formed of the area including the elements formed by rays12, 13, 14 and 15 in the same rows 3 and 4. Text pixel TP-35 is formedof the area including the elements which are formed by rays 16, 17 and18 in the same rows 3 and 4. And text pixel TP-36 is formed of the areaincluding the elements formed by rays 19, 20, 21 and 22 in the same rows3 and 4.

Every text pixel of the field of text pixels across the entire imagingarea of the member 64, of which the text pixels TP1-TP48 illustrated inFIG. 13 are representative, may be operated on in one of four ways, ashas been described hereinbefore. These four ways result from the binarycombination of one information bit and one control bit of each digitalword of the text data. These four states or conditions are divided intotwo modes, the normal mode and the reverse mode. In the normal mode thetext data may inhibit the formation of rays in any text pixel, thisresults in leaving the area of that particular text pixel charged, sothat it will be toned and will print solid upon a receptor. The secondstate of the normal mode is where the text data enables the formation ofrays under control of the graphic data. The first condition of thereverse mode or third state causes the formation of rays in the area ofa text pixel to form a clear text image in a field of a graphics image.On the receptor then, the text will be clear within the field orconfines of the printed image. The second condition of the reverse modeor the fourth state where the text data enables the formation of raysunder control of the graphics data to produce a graphics imagerepresented thereby.

It therefore may readily be seen that the second conditions of thenormal and reverse mode simply allow the formation of the graphics imagecarried by the graphics data. The first condition of the normal modeinhibits the formation of any rays or discharge elements in the entirearea of the text pixels, and the first condition of the reverse modecauses the formation of rays or discharge elements in a text pixel. Themember 64 may be imaged with text data to obtain a resolution which isthree times finer than that obtainable using the graphics pixels.Further, the text and graphics data does not have to be speciallyformated; nor does the electronics have to be construed or arranged toswitch back and forth between the text and graphics data.

In a manner similar to the predefined positions of the dischargeelements of the graphics pixels, there are predetermined centeringpoints or positions for the discharge of elements in the text pixels. Itmay readily be ascertained by viewing FIG. 13 that not all of theformable elements in a text pixel need be formed or discharged to clearthe total area of a text pixel during the first condition of the reversemode, only half of the formable elements need actually be formed withthe overlap clearing areas of the unformed elements. In fact, it may beobserved in FIG. 13 that only half of the dischargable elements in anyone text pixel need be discharged to discharge the entire area of thattext pixel. This is illustrated in text pixel TP-43 wherein there arefour discharged elements represented by the four circles 218. Thus, itmay be ascertained that by discharging the elements whose centeringpoints have an x or crossed line, as is illustrated in text pixelsTP31-TP36, the entire areas of those text pixels may be discharged.Thus, it may be seen in the reverse mode, in the condition which causesthe formation of rays to discharge the areas of the text pixels, onlyevery other ray need be formed in any one row of dischargable elements,while in the next successive row only those elements which were notformed in the preceeding row need be formed. Thus, in text pixel TP31,rays 2 and 4 are formed in row 3 while rays 1 and 3 are formed in row 4.Thus, to perform the reverse mode function which causes the formation ofrays to discharge elements of the text pixel, the electronics need onlyform alternating rays in alternating rows. The formation of these raysin the reverse mode then may be described as text reverse mode odd andtext reverse mode even, the odd and even referring to the desired rayswhich are to be formed in the even numbered rows and the rays which areto be formed in the odd numbered rows. The implementation of this oddand even arrangement will be discussed more fully hereinafter inconjunction with the electronics.

The text data is used to form solid printing areas such as foralphanumerics on a receptor and further may be used to print on areceptor line graphics such as engineering drawings, charts, graphics,etc.

There are two sets of electronic systems for the apparatus of theinvention, each electronic system being dedicated and acting inconjuction with only the left- or right-hand optical system. Theelectronics system is required to receive graphics and text data andapply radio frequency signals to the acousto-optic deflector 54, whichdischarges incremental areas on the electrophotographic member 64. Bothelectronics systems perform the same functions and are identical to eachother in all respects so that a description of one electronic system isa description of the other electronic system, and reference to anelectronic system in conjunction with the modulation of the laser beamrefers to electronic systems of the left- and right-hand opticalsystems.

The electronics system illustrated in FIG. 1 generally illustrates theoperation of both the electronic systems while the electronics systemillustrated in FIG. 14 is a more detailed illustration of the same.

Data is input to the electronics system on input leads 250, which areillustrated with arrows having a substantial width to illustrate thatthe input data is comprised of digital words having several parallelbits conveying the desired information. In the preferred embodiment thedata is input to graphics data buffers 32 and 34 and text data buffers36 sequentially, that is to say that buffer 32 is loaded first, buffer34 is loaded next and then buffer 36 is loaded last. The data containedin each buffer is the information or density values required to formgraphics pixels along one scan line and the information required to formtext pixels across an entire image line. Inputting of the data to thebuffers 32, 34 and 36 may be under control of such as a centralcontroller 252 by way of leads 254. Central controller 252 may beinterfaced with whatever system that the text and graphics data aresupplied from and may take the form of a hard wired controller or aprogrammable controller as is desired. In the preferred embodiment,central controller 252 is a programmable microprocessor.

During an initialization period before the actual text and graphics dataare input to the apparatus, the patterns that are to be selected by thegraphics data are loaded into the pattern generators 38 and 40 by way ofinput lead 250 under control of central controller 252. In thisinitialization period, data in form of the patterns that are to beloaded in the generators 38 and 40 are input into buffers 32 and 34 andare carried on leads 42 and 44, and leads 256 and 258 to the inputs ofpattern generators 38 and 40 indicated by arrow heads 260 and 262. Thus,it may be determined that pattern generators 38 and 40 comprise memorydevices that may be written into, such devices being called randomaccess memories or RAM. Loading of the pattern generators 38 and 40 isunder control of central controller 252 by way of lead or leads 264.Gating is provied that will be described hereinafter so that thegraphics data carried by leads 42 and 44 to pattern generators 38 and 40will not interfere with the patterns output by generators 38 and 40.After the initialization period has been completed and all the patternsare loaded into the pattern generators, the operational period of theimaging cycle is commenced in which the pattern generators become outputdevices.

Generation of the patterns is in response to graphics data applied topattern generators 38 and 40 by way of leads 42 and 44. Control of thegeneration of patterns and inidcation of the location of fine beam 62along the scanning line occurs by way of leads 264 from centralcontroller 252. Central controller 252 is connected to optical gratingsystem 150 by way of leads 266.

The output of pattern generators 38 and 40 are applied on leads 48 and50 to beam logic 46 which also has text data applied thereto over leads52. Control of the beam logic 46 including indication of the position offine beam 62 along the scan line is from central controller 252 overleads 268.

In the beam logic 46 the modulation of the graphics patterns to beformed at the individual rows are modulated by the text data as has beendescribed hereinbefore with the output of the beam logic on leads 56comprising the radio frequency signals required to produce the imageindicated by the combination of the text and graphics data. Generationof the fine beam 62 and reference beam 118 is as has been previouslydescribed and therefore need not be redescribed. It suffices to say thatoptical path 270 illustrated in FIG. 14 generally comprises the opticalelements between the acousto-optic deflector 54, the electrophotographicmember 64 and the optical grating system 150.

Turning now to FIG. 15, the pattern generators 38 and 40 are morespecifically shown as is the gating required to load pattern generators38 and 40 during the initial period. Latching line driver 280 is appliedwith data on leads 256, which in FIG. 15 is represented by a single linefor clarity of the drawing. During the initial period in which patternsare loaded into pattern generator 38, the latching line driver 280 undercontrol of leads 282 passes the data on leads 256 therethrough to beinput by channel A pattern RAM 284 which is placed in the read mode bylead 286. In a like manner, data which is supplied on leads 258 isapplied to latching line driver 286. During the initial period, the datapasses therethrough and is input by channel B pattern RAM 288. Channel Bpattern RAM is placed in the read mode also by lead 286. At the end ofthe initial period and at the commencement of the operation of theimaging cycle, latching line drivers 280 and 286 have their outputsplaced in a tri-state or high impedance level that places no load onleads 260, 48, 50 and 262. Thus, in the operational period the dataappearing on leads 48 and 50 will be only the outputs of pattern RAMS284 and 288.

During the operational period, graphics data is supplied to patterngenerators 38 and 40 by way of leads 42 and 44. The graphics data isinput to channel A latching counter 290 and channel B latching counter292, respectively, in the form of parallel words having 8 bits ofinformation each. The outputs of each of latching counters 290 and 292are 11 bits of information the 8 most significant bits of the outputbeing the same as the graphics data input thereto and the three leastsignificant bits being generated in response to clock signals from theoptical grating system. Loading of latching counters 290 and 282 isunder control of a load lead 294.

To understand the selection of the patterns from the pattern RAMs 284and 288, it must be understood that the value carried by each graphicsdata word represents a scaled density of an incremental area which is tobe produced or reproduced on member 64. It further will be remembered asis illustrated in FIGS. 12 and 13, the graphics pixels have a patternproduced in five sequential rows, the sixth row being used to spacebetween graphics pixels. Thus to form one pattern in a graphics pixel,information must be applied to the acousto-optic deflector 54 one row ata time to form the individual rays or beamlets required to discharge theelemental areas and produce the pattern indicated by the pattern RAMS284 and 288. In the preferred embodiment, this generation of thepatterns across the five rows of the graphics pixels occurs by using thevalue of the graphics words to select a group of addresses in thepattern RAMS 284 and 288. Then, a row clock signal produced from thesignals produced by the optical grating system 150 is used to clock orstep through the selected group of addresses. The outputs of the patternRAMS 284 and 288 at each step of the group of addresses then are thebinary indications of whether an individual ray is to be formed or not.Simply stated, the graphics words are used to select a group of memorylocations while a row clock is used to step through the locations. Theoutputs of the pattern RAMS, step by step, is the information needed toturn on or off the individual rays in fine beam 62.

The inputs to latching counters 290 and 292 are indicated as graphicsdata bits GD1-GD8. The outputs of latching counters 290 and 292 and theinputs to pattern RAMS 284 and 288 respectively are indicated asA-channel address leads AA0 through AA10 and B channel address leads BA0through BA10. The output of pattern RAMs 284 and 288 are indicated asbeing pattern bits pb1 through pb11, and pb12 through pb22. The rowclock signals for latching counters 290 and 292 respectively are appliedon leads 296 and 298.

The least significant input bits 300 and 302, respectively, of latchingcounters 290 and 292 are tied to ground. When counters 290 and 292 areloaded with data by the signal on lead 294, the outputs AA0 to AA2 andBA0 and BA2 are at zero logic levels. Thus, when row clock signals areapplied on leads 296 and 298, latching counters 290 and 292 respectivelycount up in binary manner from 0. Referring back to FIGS. 11, 12 and 13,the rows are numbered as binary numbers from 0 to 5, which correspondsrespectively to the counts produced at the outputs of latching counters290 and 292. The rows for the A and B channels of graphics data areshifted relative to one another to form the desired irregular hexagonshaving apices interleaved between one another. The clocking of thechannel A latching counter 290 thus commences earlier than the clockingof the channel B latching counter 292 to provide the patterns from therespective RAMS at the proper times.

The leads 282, 286, 294, 296 and 298 used to control the functions ofthe latching line drivers and pattern generators generally are the leads264 indicated earlier in FIG. 14 coming from central controller 252.

In FIG. 16, there is illustrated in more detail the beam logic 46.Pattern bits pb1-pb22 are applied to a 22 bit one-of-four multiplexer304 on leads 48 and 50.

While multiplexer 304 is indicated as being one unit, which is able toselect between one of four inputs, in the preferred embodimentmultiplexer 304 is a plurality of multiplexers which may be individuallyor jointly operated upon. Beam logic 46 further comprises three switcharrays 306, 308 and 310, each of which supplies 22 individual leads oflogic signals with each of the logic signals being controlled by aresistor switch network such as is illustrated in each blockrepresenting the switch arrays. Basically, the network consists of theoutput lead being tied to a plus-5 volt source through a 1-K resistor,there being a programmable switch which may be closed to short theoutput lead to ground. When the switch is open, the logic level of theoutput of the switch is a logic state one; while when the switch isclosed the output is a logic state zero.

Array 306 is labelled as being the text reverse even switch arrayindicating that the outputs of this array indicate which of theindividual rays are to be formed during a reverse mode even rowcondition indicated by the text data. The array 308 is labelled as beinga text reverse odd switch array, the label indicating that the outputsof this array indicate the individual rays which are to be formed duringa reverse mode odd row condition indicated by the text data. Array 310is labelled as being a text normal switch array with its outputsindicating the rays that are to be inhibited. The outputs of each array,TRE1-TRE22, TR01 TR022 and TN1-TN22 are applied to the inputs ofmultiplexer 304 over leads 307, 309 and 311, respectively.

Text data represented by text data bits TD1-TD8 on lead 52 of FIG. 16are applied through a gating circuit 314 to the A and B select inputs ofmultiplexer 304 on leads 316 and 318. Also applied to gating circuit 314is address lead AA0 from the A channel latching counter 290.

The outputs of multiplexer 304 are indicated as being ray data RD1-RD22,each output corresponding to the formation of an individual ray of finebeam 62 in acousto-optic deflector 54 from beam 60. The outputs ofmultiplexer 304 pass on lead 320 to a 22 bit latch 322 that holds theoutput ray data in response to a latch signal on lead 324. The output ofthe 22 bit latch is applied through leads 326 to 22 individual bitdrivers 328, there being one individual bit driver for each of theoutput bits RD1 through RD22. The 22 bit drivers are enabled by a signalon lead 330 and provide their outputs by way of leads 332 to 22 RFoscillators 334, there being one RF or radio frequency oscillator foreach of the signals from bit drivers 328 and the outputs of the 22 RFoscillators 334 appearing on leads 56 and being applied to acousto-opticdeflector 54.

In operation of the beam logic circuit, instead of there being astraight forward gating of the pattern bits PB1-PB22 by the bits of thetext data TD1-TD8, the bits of the text data are used to select, foreach of the groups of individual rays indicated in FIG. 13, between thefour inputs to multiplexer 304, i.e., graphics pattern bits, reversemode even bits, reverse mode odd bits, and normal mode bits. But to thisextent the illustration of multiplexer 304 in FIG. 16 as selectingbetween one of the four inputs for all of the ray data bits is somewhatmisleading.

A better illustration of the multiplexing that occurs is illustrated inFIG. 18, with FIG. 17 illustrating in chart form the bits of the textdata that are used to modulate the individual rays. In FIG. 18, a one offour multiplexer 336 has four groups of input bits, one group for eachof the ray data bits output therefrom. From FIG. 17, text data bit TD1is used to operate on or select the proper output for rays 1-4. As anexample, thus, the outputs of one of four multiplexer 336 are indicatedas being the ray data bits RD1 through RD4, these of course being thelogic signals which determine whether or not rays 1-4 are formed or not.To produce ray data bit RD1, multiplexer 336 may select one of patternbit pb1, text reverse even bit TRE1, text reverse odd bit TRD1 and textnormal bit TN1. Multiplexer 336 may make a similar selection for each ofray data bits RD2-RD4. It should be remembered that when the ray databits are such as a logic state 1, they indicate that an individual rayshould be formed in fine beam 62, while when the ray data bits are at alogic state zero (0), they indicate that no individual ray should beformed in fine beam 62.

Gating circuit 314 is illustrated more fully in FIG. 18. The binarycombination of a control bit (text data bit TD7) and an information bitsuch as text data bit TD1 are used to select between the four inputs toprovide an output. Gating circuit 314 also provides for the turning onof the desired individual rays during a reverse mode in the even and oddrows.

When the TEXT MODE signal is a logic state one, indicating that the beamlogic is out of the text mode, and is applied to NOR gate 340 on lead324, then the output thereof is a logic state zero, which is applied toAND gates 344 and 346 on lead 348. The outputs of AND gates 344 and 346thus are logic states zero and are applied to the A and B inputs ofmultiplexer 336, which selects the pattern bits pb1-pb4 to be output asthe ray data bits RD1-RD4. The same selection occurs when the TDl inputto NOR gate 340 is at a logic state one indicating that the pattern bitspb1-pb4 generated by the graphics data are to be formed by the raysR1-R4. When the TEXT MODE signal is at a logic state zero and the textdata bit TD1 is at a logic state zero, the output of a NOR gate 340 is alogic state one that enables AND gates 344 and 346 to provide signalswhich will select other than the graphics data bits pb1-pb4 to be formedby the rays R1-R4.

In such a case, if signal TD7 is at a logic state one, indicating anormal mode, then the outputs of OR gates 350 and 352 also will be alogic state one, which are applied, respectively, by way of leads 354and 356 to AND gates 346 and 344. The outputs of AND gates 344 and 346will then both be logic state one, which will select as the ray databits RD1-RD4 the logical levels appearing on the text normal signalsTN1-TN4. The outputs from the text normal switch array 310 illustratedin FIG. 16 thus must be programmed in logical states.zero so that theformation of individual rays R1-R4 is inhibited, areas on member 64 willremain charged, and will print solid on the receptor. Switch arrays 306,308, 310 will be understood to be provided in the preferred embodimentfor versatility of the apparatus.

In the case where the TEXT MODE signal on lead 342 and the logic levelof bit TD1 are logical states zero, if the TD7 signal is a logical statezero indicating the reverse mode, then the outputs of OR gates 350 and352 will be controlled by the logical level input thereto by the Achannel address bit zero, AA0. Signal AA0 is continuosly oscillatingbetween a logic state one and zero, as the fine beam 62 is passed acrossthe surface of the electrophotographic member 64. When bit TD7 is alogical state zero, the output of OR gate 350 is directly controlled bythe logical level of signal AA0 while the output of OR gate 352 is theinverse thereof due to inverter 358. For an even row, the outputsprovided by AND gates 344 and 346 will be such that multiplexer 336outputs as ray data bits RD1-RD4 the logical levels appearing at thesignals TRE1 through TRE4. At an odd number row, the logic levels outputby multiplexer 336 as ray data bits RD1-RD4 will be the logical levelsappearing at signals TR01-TR04.

The one of four multiplexer 336 used to form the ray data bit RD1-RD4 isan example of one of the multiplexer circuits used to provide the raydata bits for one of the groups of rays illustrated in connection withthe text pixels of FIG. 13. The gating circuit 314 also is the same foreach of those multiplexer circuits, with only the information bit TD1being changed to the corresponding text data bit for the particulargroup of rays indicated by the chart in FIG. 17.

After the electrophotographic member 64 has been charged at chargingstation 70 and has been imaged with fine beam 62, the latent imagecarried thereon is toned at toning station 72.

The purpose of the vertical toning system is to apply toner (carrierfluid having toner particles suspended therein) to theelectrophotographic member 64. The areas of member 64 that remaincharged after imaging are the areas which accept the toning particles.The toned member thereafter has the toned particles fused to the memberfor use as a printing plate in such as a lithographic printing press,but this fusing step occurs otherwise than in the apparatus.

The toner that is supplied to the member 64 is in the form of a carrierfluid known as "ISOPAR", which is a registered trademark of the ExxonCorporation. The carrier fluid carries finely ground particles ofresinous material which may be positively or negatively charged and inthe preferred embodiment herein the particles are positively charged.Hereinafter, the term "toner fluid" will refer to this carrier fluidcontaining the resinous toner particles while the term "carrier fluid"will refer only to the "ISOPAR" without the resinous particles.

As the member rotates past the toning station 72, there is first appliedthereto a quantity of carrier fluid that wets the surface of the member.This wetting of the surface occurs at what may be called an upperchamber of the toning station 72. Thereafter, the toner fluid is appliedto the member into phases which may be referred to as the initializationphase and the operational phase. During the initialization phase, ameniscus of toner fluid is established between toning station 72 andmember 64, while during the operational phase, the meniscus ismaintained between the toning station 72 and the member. Toning station72 is arranged essentially vertical adjacent the circumference of drum66, and thereby the meniscus established between toning station 72 andmember 64 is essentially vertical.

Turning now to FIG. 19, the toning system is indicated generally by thereference character 400. The toning station 72 comprises left and righthand shoes 402 and 404, respectively, that are used to apply the tonerfluid to the member 64, and it is between the shoes and the member 64that the vertical meniscus is established and maintained. The left-handshoe 402 is used in conjunction with the left-hand optical system 82,while the right-hand shoe 404 is used in conjunction with the right-handoptical system 84. An explanation of the toning system for theright-hand optical system is an explanation of the toning system for theleft-hand optical system, the toning systems for both sides beingduplicates of one another. FIG. 19 is a block diagram of one of theleft- and right-hand toning systems.

During the initialization phase, carrier fluid is supplied fromreservoir system 406 to the right-hand shoe 404 by way of tubing 408under action of pump 410. Pump 410 operates in response to or undercontrol of controller 412 by way of lead 414. Toner fluid is carried toright-hand shoe 404 from the pressure system 416 by way of tubing 418under control of pump 420, pump 420 being controlled in turn bycontroller 412 by leads 422. Excess toner fluid is returned to pressuresystem 416 from right-hand shoe 404 by way of tubing 424.

Used toner fluid is carried to sump system 426 by way of tubing 428,sump system 426 providing a vacuum or having a vacuum with which toremove the used toner fluid from the member. Used toner fluid containedin sump system 426 may be returned to the reservoir system 406 by way oftubing 430 by action of pump 432, pump 432 in turn being controlled bycontroller 412 by way of leads 434.

After the meniscus has been established during the initialization phase,valve 436 is used to admit air into pressure system 416 over tubing 438to aid in the maintenance of the meniscus between the shoe 404 and themember 64.

It is important that the application of the carrier and toner fluids andthe operation of the vacuum sump system occur at the proper timeintervals as the member 64 is rotated past the shoe 404. A sensor 440 iscoupled to drum 66 to obtain the timing information and supplies thetiming information to controller 412 by way of leads 444.

The toning station 72 is generally illustrated in FIG. 20 wherein leftand right hand shoes 402 and 404 are carried by backplate 440. Thebackplate 440 carries four rollers, 442, two at each end that are inrolling contact with drum 66 along surfaces 444. Rollers 442 areadjustable by way of a cam mounting to adjust the spacing between shoes402, 404, and drum 66. The spacing required between the shoes 402, 404and drum 66 must be sufficient for the electrophotographic member 64 topass therebetween with sufficient spacing to provide for the meniscus oftoner fluid established therebetween.

Toning station 72 has two positions, one being with the rollers engagedagainst the surfaces 444 of drum 66 during an imaging and toning cycle,and the other position being spaced from the drum and at a level belowthe drum in a non-toning position. A pneumatic or hydraulic cylinder 446is provided to move the toning station 72 between these two positionsand further is used to provide a slight bias to maintain rollers 442 incontact with surfaces 444. Rollers 442 are engaged against surfaces 444at the two longitudinal ends of drum 66 so as not to intefere withmember 64 which is carried on drum 66. Of course, any surfaces as may bedesired may be provided upon which the rollers of plate 440 may ride.

In FIG. 21 right-hand shoe 404 is essentially a rectangular solid with asurface 446 that is to be placed adjacent the drum 66, surface 446having a portion 448 which is concave. The radius of this concaveportion 448 is essentially equal to the radius of the drum 66 so thatthe concave portion 448 may be spaced equidistant from drum 66 acrossits entire area.

A generally H-shaped seal member 450 is carried on shoe 404 at theconcave portion 448. Seal member 450 has vertical standards arrangedadjacent the curved edges of concave portion 448 with the cross bar 452of the "H" being offset towards the top of the seal. The seal is madefrom a resilient material such as polyurethane and is mounted into slotsextending into the shoe. The seal is constructed so that when the shoe404 is in the toning position, the edges of the seal 450 extendingfurthest from the shoe are engaged against the outer surface of theelectrophotographic member 64.

The cross-bar 452 of the seal 450 separates the concave portion 448 intoupper and lower portions 454 and 456. In the upper portion 454, clearcarrier fluid is applied to the member 64. This provides a precoating orwetting of the member 64 with this precoating acting as a barrieragainst toner particles that are not charged becoming lodged on themember 64 to reduce fogging of the latent image. This precoating furtherprovides a lubricant for the seal 450 to reduce wear of the seal,improve the sealing characteristics thereof and reduce the power whichwould otherwise be required to be supplied by motor 90 to drive the drum66.

Cross-bar 452 is constructed to provide a wiper blade portion 458 FIG.22 that allows only a microscopic coating of the carrier fluid to remainon the member 64 as it passes thereby. Of course, the wiper bladeportion 458 as it is wiped across the member 64 does not disturb thequality of characteristics of the latent image carried thereon. It willfurther be appreciated that the carrier fluid applied in upper portion454 does not affect the quality or characteristics of the latent imageon member 64.

The upper portion 454 comprises an upper chamber 460 extending into shoe404 and opening to concave surface 448. Supply ports 462 are arrangedspaced from one another along the inner wall of the upper chamber 460 tosupply carrier fluid transported by tubing 408 from reservoir system 406for application to the member 64. A baffle 464 shown in FIG. 22 iscontained in upper chamber 460 so that carrier fluid from ports 462 maybe evenly supplied to member 64 across the length of chamber 460.

The lower portion 456 of the concave portion 448 is the portion wheretoner fluid is applied to member 64. A lower chamber 466 extends intoshoe 404, is open to concave portion 448 and extends essentially thelength of the shoe. Toner fluid is supplied to lower chamber 466 by theway of inlet ports 468 spaced along the length of chamber 466 with thetoner fluid being supplied from pressure system 416 by way of tubing418. A baffle 470 may be provided in lower chamber 466 to evenly supplytoner fluid to member 64 from the individual inlet ports 468.

From lower chamber 466, toner fluid may flow down in the directionindicated by arrow 472 in FIG. 22 along concave portion 448 to vacuumslot 474.

A reduction in atmospheric pressure or a vacuum is created at vacuumslot 474 by sump system 426 (FIG. 19) by way of tubing 428. This vacuumoperates to remove toner fluid from both member 64 and shoe 404 as thetoner fluid flows down along the concave portion 448. From vacuum slot474, toner fluid is carried to sump system 426 by tubing 428. The vacuumprovided by sump system 426 may be formed by any means desired.

Outlet ports 476 are provided opening from lower chamber 466, spacedalong the length of lower chamber 466 and against an upper wall thereof,as is illustrated in FIG. 22. Outlet ports 474 provide for return ofexcess toner fluid by way of tubing 424 to pressure system 416.

FIG. 22 generally illustrates the angular relationship between chargingstation 70, the incidence of fine beam 62, the member 64 and theposition of shoe 404. In the preferred embodiment, the angle A betweenthe center line of charging station 70 and fine beam 62 is about 25°.The angle B between fine beam 62 and the center line of shoe 404 isabout 30°. While these angles are indicative of the preferredembodiment, it is desired to reduce these angles to be as small aspossible so that there is a minimum time between the charging of themember 64 and the toning of the latent image on member 64.

Charging station 70 comprises a charging wire 480 with a guard 482forming a three-sided channel which is open towards drum 66. Wire 480 ofcourse extends along the length of drum 66 as does guard 482. In thepreferred embodiment, wire 480 carries a negative voltage and cover 482may be made of conductive material and forms an electrostatic mirror.

Area 484 along the interface between drum 66 and 244 is shown enlargedin FIG. 23 to illustrate the relative positions between drum 66,electrophotographic member 64, toner fluid 486 and shoe 404. Therelative thicknesses of the elements are expanded in FIG. 23 forillustrative purposes.

The operation of the toning system may best be understood by consideringthat there are phases to its operation. After the member 64 ispre-wetted with carrier fluid, the first phase occurs and is known asthe initial phase. During this phase, the toner system establishes ameniscus of toner fluid between shoe 404 and member 64. During theoperational phase, which occurs next, this meniscus is maintainedbetween member 64 and shoe 404 and flows in the direction indicated byarrow 472 at a controlled rate essentially equal to the angular rotationof the drum. Thus, as member 64 is moved past chamber 466, a quantity oftoner fluid is applied against member 64 and remains stationary relativeto member 64, until it is removed at vacuum slot 474. This provides aminimum amount of sheer between the meniscus and member 64 whichprovides for suitable toning of the latent image with the toningparticles.

At this point, it will be discussed how the pre-wetting reduces thefogging of the latent image. The toner fluid, as has been said, containstoner particles or resinous material. These particles are very sticky inthat they will readily adhere to most any surface they are brought intocontact with. When the toner fluid is manufactured, these particles aregiven in this case, a positive charge so that they will be attractedonly to the areas which retain their negative charge from chargingstation 70. Not all of these particles however, remain charged by thetime they are used in the toning system herein.

When the toning fluid is used in the toning system, the chargedparticles readily are attracted to the oppositely charged areas of thelatent image carried by member 64. The non-charged particles however,are not so attracted and will stick to any surface to which they maycome into contact with. By pre-wetting the surface of member 64, abarrier is formed through which these non-charged particles generallywill not pass. Although this pre-wetting provides what is referred to asa barrier the action that is involved is more along the lines of thenon-charged particles not passing through the pre-wet because there isno force that will drive them through the barrier.

During the commencement of the toning cycle, toner fluid is applied tothe lower chamber 466 and falls essentially by means of gravity into thespace established between concave portion 448 and member 64. The rate atwhich toner fluid is supplied to chamber 466 is much greater than therate at which toner fluid may flow between concave surface 448 andmember 64 with excess toner fluid being returned to the pressure system416 through the outlet ports 476 by way of tubing 424. Pressure system416 is sealed from the atmosphere and as toner fluid is removed from thepressure system by way of the meniscus which is formed between concavesurface 448 and member 64, a negative pressure is formed in the pressuretank. When this negative pressure reaches a magnitude of from two tothree inches of water, the toner fluid ceases to flow between theconcave surface and the member 64. Air control valve 436 is preset toallow a controlled and predetermined amount of air into the closedpressure system 416, and then controls the flow rate of the toner fluidin the meniscus between the concave surface 448 and member 64.

If the air flow control valve 436 were to be closed, the meniscus wouldessentially remain stationary in the vertical position discounting ofcourse losses from the lower edge thereof occurring from gravity andfrom the vacuum slot 474. As the air flow control valve 436 is opened,the rate of flow of toner fluid through the vertical meniscus increases.The establishment of this negative pressure in the pressure system 416and the simultaneous establishment of the meniscus between concaveportion 448 and member 64 is what has been defined to be the initialphase. Once the initial phase is completed, operation of the toningoccurs through what has been described the operation phase. It should beunderstood that there are not two separate phases that are in operationin the toning system, but rather two phases that are used to describethe operation of the toning system.

The rate at which air is allowed into the pressure system 416 throughcontrol valve 436 is predetermined so that the flowrate of toner fluidtherebetween occurs at the same speed as the angular rate of rotation ofdrum 66. Thus, the toner fluid flows essentially stationary to themember 64. As the lower edge of the meniscus approaches the vacuum slot474, toner fluid less the toner particles attracted to the member 64 bythe latent image is removed from the member 64 with the describedvacuum.

In summary, the vertical toning system provides a meniscus of toningfluid which is essentially stationary relative to the movement of theelectrophotographic member member 64 to provide toning of the latentimage on the member 64. Control of the flow of the meniscus relative tothe member may be easily controlled through a suitable air control valve436 and the toner fluid is applied to member 64 after a period of timewhich is relatively short after imaging of the member has occurred.

Clear carrier fluid is indicated in upper chamber 460 by referencecharacter 490, while toner fluid is indicated in the lower chamber 466by reference character 486.

In the preferred embodiment, the meniscus has a thickness or the concaveportion 48 is spaced from member 64 a distance of about 13/1000 of aninch. Shoe 404 may be made of any material which is nonreactive to the"ISOPAR" carrier fluid, such as aluminum or stainless steel. It furthershould be noted that when the toning station 72 is removed from beingadjacent drum 66 to the non-toning position, the vacuum which is createdat vacuum slot 474 is increased to clear off both the shoe and themember.

It is important that the commencement of the flowing of the carrierfluid and toner fluid to the shoe occur at the proper time inrelationship to the movement of the member 64 across the shoe 404. Ifthese fluids are applied to the shoe too early, they are not containedwithin the seals provided by seal member 450 and may cause a mess whileif the fluids are applied too late, the seals may stick to the member64.

Referring back to the two toner shoes 404 and 404, it is entirelypossible that one toning shoe could be used in place of the two shoes.

Modifications and variations of the present invention are possible inlight of the above teachings. It is therefore to be understood thatwithin the scope of the claims the invention may be practiced otherwisethan is specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. A field flattening lens system for use in an optical imaging system,said system including a raster mirror, oscillating from side to sidearound a vertical axis, an elongate member to be imaged, said memberbeing imaged along a horizontal image line which is spaced from saidvertical axis, and a focused beam of light traveling along an opticalpath approaching said raster mirror in a straight line and leaving saidraster mirror along a straight line that is swept from side to side in aplane by oscillation of said raster mirror, said plane including saidhorizontal image line, said lens system comprising:a plurality of lenscomponents arranged between said raster mirror and said member with saidoptical path passing therethrough, the lens components including fromthe object to the image end a first negative component having a concaveobject side surface, a second positive component having a concave objectside surface, a third positive component having a substantially flatobject side surface and a fourth component having a flat object sidesurface, the lens components providing unitary magnification andmaintaining said beam in focus at said image line along said elongatemember as said optical path leaving said raster mirror is swept fromside to side, each component being made from a material having a lowindex of refraction.
 2. The lens as claimed in claim 1 definedsubstantially by the following data, where the components L1, L2, L3 andL4 comprise respectively the first, second, third and fourth components:

    ______________________________________                                                         Axial Distance                                               LENS  Radius     Between Surfaces (mm)                                                                           N.sub.d                                                                            V.sub.d                               ______________________________________                                            R1    -161.744                                                            L1                   15.00           1.617                                                                              36.6                                    R2    ∞    6.97                                                         R3    -216.311                                                            L2                   28.871          1.523                                                                              58.6                                    R4    -213.119                                                                                 0.20                                                         R5    -2575.204                                                           L3                   18.06           1.523                                                                              58.6                                    R6    -264.288                                                                                 0.20                                                         R7    ∞                                                             L4                   13.00           1.523                                                                              58.6                                    R8    -265.847                                                            ______________________________________                                    

where L1-L4 are lens components from the object to the image end, R1-R8are the radii of the surfaces of the lens components, N_(d) is the indexof refraction, and V_(d) is the Abbe number of components L1 through L4.